I HATE THEM.
RPC
Not that I really hate them... But wouldn't it be better if you have this awesome character you made be in an awesome manga that you made? I mean... RPC's are really just abusing the character(no offense).I mean, it's basically just editing a character right? And wouldn't it be upsetting if you made a character, and someone edited it and called it their own? It's like having your photo edited to make another person. Not that I hate the RPC artist but, I personally think it would be better that a character will have it's own style in illustration.

OC
OC's are cool. But not when you insert them in anime's that YOU did NOT make. It's like changing the storyline. I have seen many OC's inserted in Naruto. Usually the OC represents themselves and pair them with guys (ex. SasukexOC, NarutoxOC). Two words, NOT COOL. It REALLY REALLY would be better if you just made your own story/manga with a character that resembles them and add you OC. Now that would be called original and creative. Which brings a new meaning to OC.

Mary Sues
I hate this the most. It's when you add characters you made that are just PERFECT. And pair them up. Disgusting. Its basically and OC and an RPC put together in one PERFECT character. Usualy the are paired, and the person they are paired to falls in love with them the first second they meet. It's really annoying how people make up their own Mary Sues.

P.S. If you are offended in what I have said, please don't put rude, nasty comments. Just speak politely

I do not mean to offend anyone here. Just saying what I think.